There are two tests that can do done. To determine whether your own insulin is too high or too low, the c-peptide test can be done. The other is the GAD test which checks for antibodies that can destroy islet cells. As a great generalisation, it you have excess weight then you are likely to be T2 and have too much insulin which the body can't use due to insulin resistance build-up in the muscle cells. Having a low-carb diet should reduce the weight and be an indicator to what the problem is. If you are slim or have lost weight unexpectedly recently then you may well be a Late onset T1 and have low insulin. The two tests are quite expensive and GPs can be reluctant to do them; I had mine done privately.
